The present invention relates to piezoelectric transformers, and in particular to a transformer comprising a single crystal piezoelectric material.
Piezoelectric transformers have been known for many years, and are described, for example, in U.S. Pat. No. 2,974,296 to C. A. Rosen. These transformers use mechanical resonance of a piezoelectric element to transform current and voltage. An input current is passed through the element, causing it to vibrate at a resonant frequency. Electrodes are attached to the element at different points from the input electrodes, thereby producing a transformed output current in response to the mechanical deformation.
Piezoelectric transformers offer a unique method of step-up and step-down voltage conversion as compared to traditional coil-based electromagnetic transformers. Piezoelectric transformers offer higher voltage gains while retaining significant current throughput in applications where a large number of coil windings and low output amperages become impractical. They operate efficiently (upwards of 90%) in a narrow frequency band (the mechanical resonant frequency), while electromagnetic transformers tend to have lower efficiencies but to operate at a broad range of frequencies.
Prior art in the area of piezoelectric transformers has focused on high mechanical Q materials to increase the voltage transmission of energy. Lower Q devices, using softer polycrystalline materials, are possible, but generally fail because they cannot support high power levels without overheating. U.S. Pat. No. 6,114,797 to Bishop et al. has proposed a combination of hard (input side) and soft (output side) materials to achieve high power throughput with lower voltage gains.
The present invention comprises a piezoelectric transformer having substantially improved performance. The piezoelectric element is composed of a single crystal of a relaxor ferroelectric piezoelectric material. This element is coupled to input and output electrodes. The element vibrates mechanically in response to an input signal, which causes an output signal to be generated at the output electrodes. Improved power transmission is observed despite the reduced mechanical Q of the single crystal material, because the coupling and dielectric strength of the material are improved relative to polycrystals.